This invention relates to non-skid surface compositions applied to the surface of a material to increase the surface friction. More particularly, this invention is directed to silica- or alumina-containing non-skid surface compositions applied to paper products such as paperboard and linerboard used in the manufacture of, for example, corrugated boxes, folding carton stock, communication paper packaging, and containers.
Corrugated boxes and containers, as well as other paper packaging products, are used in the shipment of a wide variety of goods. In many instances, the boxes and containers are stacked for storage and shipment, and the toppling of a stack may cause damage to the contents thereof.
Accordingly, it is desirable for the surfaces of paperboard and linerboard containers and boxes to have a high surface friction so that the stacked boxes will be less likely to shift and topple during handling. However, achieving a sufficiently high surface friction on paperboard products has been made more difficult in recent years because of the trend toward the use of recycled fiber in paper and liner board products, in some instances up to 100% recycled fibers may be used. The use of large percentages of recycled fibers in the finished paper has led to increasing problems in the handling of the paper, both in the mill and at converters, because of its increased slipperiness. This loss in the coefficient of friction is due to the shorter fibers which result from the additional processing required by recycling as compared to virgin paper fibers, as well as from contaminants introduced with the used paper. These contaminants include dirt, wax, cold set and hot melt adhesives, defoamers, water proofing, and other special coatings, etc. Various paper fiber processing techniques have been employed to remove some of these contaminants prior to paper formation but have had only marginal success in removing the wax-like contaminants which cause the paper to become slippery.
Thus, the combination of shorter recycled fibers and wax-like contaminants have had a detrimental effect on the finished linerboard coefficient of friction, or slip-angle, as it is commonly measured by the TAPPI methods T815-OM90 and T815-OM92. For instance, virgin linerboard will generally have TAPPI-method slip-angles of between 17.degree. and 25.degree.. Typical linerboard made with some of recycled fiber will have slip-angles of from 15.degree. to 20.degree., and some boards having a high percentage of recycled fibers, and their concomitant contaminants, can have slip-angles of between 10.degree. and 15.degree.. Slip-angles of less than 20.degree. have been found to be the cause of several paper and container handling problems.
One method used in the past to increase the surface friction of paperboard products has been to apply frictionizing agents to the exterior surfaces of the boxes and containers, typically by spraying the surfaces of the boxes with a frictionizing agent in a carrier or solvent. Such frictionizing agents increase the slip angle (a measure of surface friction) of the boxes.
For example, Carstens, U.S. Pat. Nos. 4,418,111 and 4,452,723, teach the use of a combination of an aqueous suspension of colloidal silica and urea as a non-skid agent. Payne et al, U.S. Pat. No. 4,980,024, teach the use of an aqueous antiskid composition which includes silica sol, 2 percent glycerine, and 5 percent polyacrylamide binder.
However, such prior art compositions have presented problems relating to application and clean up of the compositions. Accordingly, the need still exists in the art for a non-skid surface composition which is easy to apply and clean up, which is nontoxic and noncorrosive, and which does not affect the ability to recycle the paper to which it is coated.